//===- ASTWriter.h - AST File Writer ----------------------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

//  This file defines the ASTWriter class, which writes an AST file

//  containing a serialized representation of a translation unit.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_SERIALIZATION_ASTWRITER_H

#define LLVM_CLANG_SERIALIZATION_ASTWRITER_H

#include "clang/AST/ASTMutationListener.h"

#include "clang/AST/Decl.h"

#include "clang/AST/Type.h"

#include "clang/Basic/LLVM.h"

#include "clang/Basic/Module.h"

#include "clang/Basic/SourceLocation.h"

#include "clang/Sema/Sema.h"

#include "clang/Sema/SemaConsumer.h"

#include "clang/Serialization/ASTBitCodes.h"

#include "clang/Serialization/ASTDeserializationListener.h"

#include "clang/Serialization/PCHContainerOperations.h"

#include "clang/Serialization/SourceLocationEncoding.h"

#include "llvm/ADT/ArrayRef.h"

#include "llvm/ADT/DenseMap.h"

#include "llvm/ADT/DenseSet.h"

#include "llvm/ADT/MapVector.h"

#include "llvm/ADT/STLExtras.h"

#include "llvm/ADT/SetVector.h"

#include "llvm/ADT/SmallVector.h"

#include "llvm/ADT/StringRef.h"

#include "llvm/Bitstream/BitstreamWriter.h"

#include <cassert>

#include <cstddef>

#include <cstdint>

#include <ctime>

#include <memory>

#include <queue>

#include <string>

#include <utility>

#include <vector>

namespace clang {

class ASTContext;

class ASTReader;

class Attr;

class CXXRecordDecl;

class FileEntry;

class FPOptionsOverride;

class FunctionDecl;

class HeaderSearch;

class HeaderSearchOptions;

class IdentifierResolver;

class LangOptions;

class MacroDefinitionRecord;

class MacroInfo;

class Module;

class InMemoryModuleCache;

class ModuleFileExtension;

class ModuleFileExtensionWriter;

class NamedDecl;

class ObjCInterfaceDecl;

class PreprocessingRecord;

class Preprocessor;

class RecordDecl;

class Sema;

class SourceManager;

class Stmt;

class StoredDeclsList;

class SwitchCase;

class Token;

/// Writes an AST file containing the contents of a translation unit.

///

/// The ASTWriter class produces a bitstream containing the serialized

/// representation of a given abstract syntax tree and its supporting

/// data structures. This bitstream can be de-serialized via an

/// instance of the ASTReader class.

class ASTWriter : public ASTDeserializationListener,

                  public ASTMutationListener {

public:

  friend class ASTDeclWriter;

  friend class ASTRecordWriter;

  using RecordData = SmallVector<uint64_t, 64>;

  using RecordDataImpl = SmallVectorImpl<uint64_t>;

  using RecordDataRef = ArrayRef<uint64_t>;

private:

  /// Map that provides the ID numbers of each type within the

  /// output stream, plus those deserialized from a chained PCH.

  ///

  /// The ID numbers of types are consecutive (in order of discovery)

  /// and start at 1. 0 is reserved for NULL. When types are actually

  /// stored in the stream, the ID number is shifted by 2 bits to

  /// allow for the const/volatile qualifiers.

  ///

  /// Keys in the map never have const/volatile qualifiers.

  using TypeIdxMap = llvm::DenseMap<QualType, serialization::TypeIdx,

                                    serialization::UnsafeQualTypeDenseMapInfo>;

  using LocSeq = SourceLocationSequence;

  /// The bitstream writer used to emit this precompiled header.

  llvm::BitstreamWriter &Stream;

  /// The buffer associated with the bitstream.

  const SmallVectorImpl<char> &Buffer;

  /// The PCM manager which manages memory buffers for pcm files.

  InMemoryModuleCache &ModuleCache;

  /// The ASTContext we're writing.

  ASTContext *Context = nullptr;

  /// The preprocessor we're writing.

  Preprocessor *PP = nullptr;

  /// The reader of existing AST files, if we're chaining.

  ASTReader *Chain = nullptr;

  /// The module we're currently writing, if any.

  Module *WritingModule = nullptr;

  /// The byte range representing all the UNHASHED_CONTROL_BLOCK.

  std::pair<uint64_t, uint64_t> UnhashedControlBlockRange;

  /// The bit offset of the AST block hash blob.

  uint64_t ASTBlockHashOffset = 0;

  /// The bit offset of the signature blob.

  uint64_t SignatureOffset = 0;

  /// The bit offset of the first bit inside the AST_BLOCK.

  uint64_t ASTBlockStartOffset = 0;

  /// The byte range representing all the AST_BLOCK.

  std::pair<uint64_t, uint64_t> ASTBlockRange;

  /// The base directory for any relative paths we emit.

  std::string BaseDirectory;

  /// Indicates whether timestamps should be written to the produced

  /// module file. This is the case for files implicitly written to the

  /// module cache, where we need the timestamps to determine if the module

  /// file is up to date, but not otherwise.

  bool IncludeTimestamps;

  /// Indicates whether the AST file being written is an implicit module.

  /// If that's the case, we may be able to skip writing some information that

  /// are guaranteed to be the same in the importer by the context hash.

  bool BuildingImplicitModule = false;

  /// Indicates when the AST writing is actively performing

  /// serialization, rather than just queueing updates.

  bool WritingAST = false;

  /// Indicates that we are done serializing the collection of decls

  /// and types to emit.

  bool DoneWritingDeclsAndTypes = false;

  /// Indicates that the AST contained compiler errors.

  bool ASTHasCompilerErrors = false;

  /// Mapping from input file entries to the index into the

  /// offset table where information about that input file is stored.

  llvm::DenseMap<const FileEntry *, uint32_t> InputFileIDs;

  /// Stores a declaration or a type to be written to the AST file.

  class DeclOrType {

  public:

    DeclOrType(Decl *D) : Stored(D), IsType(false) {}

    DeclOrType(QualType T) : Stored(T.getAsOpaquePtr()), IsType(true) {}

    bool isType() const { return IsType; }

    bool isDecl() const { return !IsType; }

    QualType getType() const {

      assert(isType() && "Not a type!");

      return QualType::getFromOpaquePtr(Stored);

    }

    Decl *getDecl() const {

      assert(isDecl() && "Not a decl!");

      return static_cast<Decl *>(Stored);

    }

  private:

    void *Stored;

    bool IsType;

  };

  /// The declarations and types to emit.

  std::queue<DeclOrType> DeclTypesToEmit;

  /// The first ID number we can use for our own declarations.

  serialization::DeclID FirstDeclID = serialization::NUM_PREDEF_DECL_IDS;

  /// The decl ID that will be assigned to the next new decl.

  serialization::DeclID NextDeclID = FirstDeclID;

  /// Map that provides the ID numbers of each declaration within

  /// the output stream, as well as those deserialized from a chained PCH.

  ///

  /// The ID numbers of declarations are consecutive (in order of

  /// discovery) and start at 2. 1 is reserved for the translation

  /// unit, while 0 is reserved for NULL.

  llvm::DenseMap<const Decl *, serialization::DeclID> DeclIDs;

  /// Offset of each declaration in the bitstream, indexed by

  /// the declaration's ID.

  std::vector<serialization::DeclOffset> DeclOffsets;

  /// The offset of the DECLTYPES_BLOCK. The offsets in DeclOffsets

  /// are relative to this value.

  uint64_t DeclTypesBlockStartOffset = 0;

  /// Sorted (by file offset) vector of pairs of file offset/DeclID.

  using LocDeclIDsTy =

      SmallVector<std::pair<unsigned, serialization::DeclID>, 64>;

  struct DeclIDInFileInfo {

    LocDeclIDsTy DeclIDs;

    /// Set when the DeclIDs vectors from all files are joined, this

    /// indicates the index that this particular vector has in the global one.

    unsigned FirstDeclIndex;

  };

  using FileDeclIDsTy =

      llvm::DenseMap<FileID, std::unique_ptr<DeclIDInFileInfo>>;

  /// Map from file SLocEntries to info about the file-level declarations

  /// that it contains.

  FileDeclIDsTy FileDeclIDs;

  void associateDeclWithFile(const Decl *D, serialization::DeclID);

  /// The first ID number we can use for our own types.

  serialization::TypeID FirstTypeID = serialization::NUM_PREDEF_TYPE_IDS;

  /// The type ID that will be assigned to the next new type.

  serialization::TypeID NextTypeID = FirstTypeID;

  /// Map that provides the ID numbers of each type within the

  /// output stream, plus those deserialized from a chained PCH.

  ///

  /// The ID numbers of types are consecutive (in order of discovery)

  /// and start at 1. 0 is reserved for NULL. When types are actually

  /// stored in the stream, the ID number is shifted by 2 bits to

  /// allow for the const/volatile qualifiers.

  ///

  /// Keys in the map never have const/volatile qualifiers.

  TypeIdxMap TypeIdxs;

  /// Offset of each type in the bitstream, indexed by

  /// the type's ID.

  std::vector<serialization::UnderalignedInt64> TypeOffsets;

  /// The first ID number we can use for our own identifiers.

  serialization::IdentID FirstIdentID = serialization::NUM_PREDEF_IDENT_IDS;

  /// The identifier ID that will be assigned to the next new identifier.

  serialization::IdentID NextIdentID = FirstIdentID;

  /// Map that provides the ID numbers of each identifier in

  /// the output stream.

  ///

  /// The ID numbers for identifiers are consecutive (in order of

  /// discovery), starting at 1. An ID of zero refers to a NULL

  /// IdentifierInfo.

  llvm::MapVector<const IdentifierInfo *, serialization::IdentID> IdentifierIDs;

  /// The first ID number we can use for our own macros.

  serialization::MacroID FirstMacroID = serialization::NUM_PREDEF_MACRO_IDS;

  /// The identifier ID that will be assigned to the next new identifier.

  serialization::MacroID NextMacroID = FirstMacroID;

  /// Map that provides the ID numbers of each macro.

  llvm::DenseMap<MacroInfo *, serialization::MacroID> MacroIDs;

  struct MacroInfoToEmitData {

    const IdentifierInfo *Name;

    MacroInfo *MI;

    serialization::MacroID ID;

  };

  /// The macro infos to emit.

  std::vector<MacroInfoToEmitData> MacroInfosToEmit;

  llvm::DenseMap<const IdentifierInfo *, uint32_t>

      IdentMacroDirectivesOffsetMap;

  /// @name FlushStmt Caches

  /// @{

  /// Set of parent Stmts for the currently serializing sub-stmt.

  llvm::DenseSet<Stmt *> ParentStmts;

  /// Offsets of sub-stmts already serialized. The offset points

  /// just after the stmt record.

  llvm::DenseMap<Stmt *, uint64_t> SubStmtEntries;

  /// @}

  /// Offsets of each of the identifier IDs into the identifier

  /// table.

  std::vector<uint32_t> IdentifierOffsets;

  /// The first ID number we can use for our own submodules.

  serialization::SubmoduleID FirstSubmoduleID =

      serialization::NUM_PREDEF_SUBMODULE_IDS;

  /// The submodule ID that will be assigned to the next new submodule.

  serialization::SubmoduleID NextSubmoduleID = FirstSubmoduleID;

  /// The first ID number we can use for our own selectors.

  serialization::SelectorID FirstSelectorID =

      serialization::NUM_PREDEF_SELECTOR_IDS;

  /// The selector ID that will be assigned to the next new selector.

  serialization::SelectorID NextSelectorID = FirstSelectorID;

  /// Map that provides the ID numbers of each Selector.

  llvm::MapVector<Selector, serialization::SelectorID> SelectorIDs;

  /// Offset of each selector within the method pool/selector

  /// table, indexed by the Selector ID (-1).

  std::vector<uint32_t> SelectorOffsets;

  /// Mapping from macro definitions (as they occur in the preprocessing

  /// record) to the macro IDs.

  llvm::DenseMap<const MacroDefinitionRecord *,

                 serialization::PreprocessedEntityID> MacroDefinitions;

  /// Cache of indices of anonymous declarations within their lexical

  /// contexts.

  llvm::DenseMap<const Decl *, unsigned> AnonymousDeclarationNumbers;

  /// An update to a Decl.

  class DeclUpdate {

    /// A DeclUpdateKind.

    unsigned Kind;

    union {

      const Decl *Dcl;

      void *Type;

      SourceLocation::UIntTy Loc;

      unsigned Val;

      Module *Mod;

      const Attr *Attribute;

    };

  public:

    DeclUpdate(unsigned Kind) : Kind(Kind), Dcl(nullptr) {}

    DeclUpdate(unsigned Kind, const Decl *Dcl) : Kind(Kind), Dcl(Dcl) {}

    DeclUpdate(unsigned Kind, QualType Type)

        : Kind(Kind), Type(Type.getAsOpaquePtr()) {}

    DeclUpdate(unsigned Kind, SourceLocation Loc)

        : Kind(Kind), Loc(Loc.getRawEncoding()) {}

    DeclUpdate(unsigned Kind, unsigned Val) : Kind(Kind), Val(Val) {}

    DeclUpdate(unsigned Kind, Module *M) : Kind(Kind), Mod(M) {}

    DeclUpdate(unsigned Kind, const Attr *Attribute)

          : Kind(Kind), Attribute(Attribute) {}

    unsigned getKind() const { return Kind; }

    const Decl *getDecl() const { return Dcl; }

    QualType getType() const { return QualType::getFromOpaquePtr(Type); }

    SourceLocation getLoc() const {

      return SourceLocation::getFromRawEncoding(Loc);

    }

    unsigned getNumber() const { return Val; }

    Module *getModule() const { return Mod; }

    const Attr *getAttr() const { return Attribute; }

  };

  using UpdateRecord = SmallVector<DeclUpdate, 1>;

  using DeclUpdateMap = llvm::MapVector<const Decl *, UpdateRecord>;

  /// Mapping from declarations that came from a chained PCH to the

  /// record containing modifications to them.

  DeclUpdateMap DeclUpdates;

  using FirstLatestDeclMap = llvm::DenseMap<Decl *, Decl *>;

  /// Map of first declarations from a chained PCH that point to the

  /// most recent declarations in another PCH.

  FirstLatestDeclMap FirstLatestDecls;

  /// Declarations encountered that might be external

  /// definitions.

  ///

  /// We keep track of external definitions and other 'interesting' declarations

  /// as we are emitting declarations to the AST file. The AST file contains a

  /// separate record for these declarations, which are provided to the AST

  /// consumer by the AST reader. This is behavior is required to properly cope with,

  /// e.g., tentative variable definitions that occur within

  /// headers. The declarations themselves are stored as declaration

  /// IDs, since they will be written out to an EAGERLY_DESERIALIZED_DECLS

  /// record.

  SmallVector<serialization::DeclID, 16> EagerlyDeserializedDecls;

  SmallVector<serialization::DeclID, 16> ModularCodegenDecls;

  /// DeclContexts that have received extensions since their serialized

  /// form.

  ///

  /// For namespaces, when we're chaining and encountering a namespace, we check

  /// if its primary namespace comes from the chain. If it does, we add the

  /// primary to this set, so that we can write out lexical content updates for

  /// it.

  llvm::SmallSetVector<const DeclContext *, 16> UpdatedDeclContexts;

  /// Keeps track of declarations that we must emit, even though we're

  /// not guaranteed to be able to find them by walking the AST starting at the

  /// translation unit.

  SmallVector<const Decl *, 16> DeclsToEmitEvenIfUnreferenced;

  /// The set of Objective-C class that have categories we

  /// should serialize.

  llvm::SetVector<ObjCInterfaceDecl *> ObjCClassesWithCategories;

  /// The set of declarations that may have redeclaration chains that

  /// need to be serialized.

  llvm::SmallVector<const Decl *, 16> Redeclarations;

  /// A cache of the first local declaration for "interesting"

  /// redeclaration chains.

  llvm::DenseMap<const Decl *, const Decl *> FirstLocalDeclCache;

  /// Mapping from SwitchCase statements to IDs.

  llvm::DenseMap<SwitchCase *, unsigned> SwitchCaseIDs;

  /// The number of statements written to the AST file.

  unsigned NumStatements = 0;

  /// The number of macros written to the AST file.

  unsigned NumMacros = 0;

  /// The number of lexical declcontexts written to the AST

  /// file.

  unsigned NumLexicalDeclContexts = 0;

  /// The number of visible declcontexts written to the AST

  /// file.

  unsigned NumVisibleDeclContexts = 0;

  /// A mapping from each known submodule to its ID number, which will

  /// be a positive integer.

  llvm::DenseMap<const Module *, unsigned> SubmoduleIDs;

  /// A list of the module file extension writers.

  std::vector<std::unique_ptr<ModuleFileExtensionWriter>>

      ModuleFileExtensionWriters;

  /// Mapping from a source location entry to whether it is affecting or not.

  llvm::BitVector IsSLocAffecting;

  /// Mapping from \c FileID to an index into the FileID adjustment table.

  std::vector<FileID> NonAffectingFileIDs;

  std::vector<unsigned> NonAffectingFileIDAdjustments;

  /// Mapping from an offset to an index into the offset adjustment table.

  std::vector<SourceRange> NonAffectingRanges;

  std::vector<SourceLocation::UIntTy> NonAffectingOffsetAdjustments;

  /// Collects input files that didn't affect compilation of the current module,

  /// and initializes data structures necessary for leaving those files out

  /// during \c SourceManager serialization.

  void collectNonAffectingInputFiles();

  /// Returns an adjusted \c FileID, accounting for any non-affecting input

  /// files.

  FileID getAdjustedFileID(FileID FID) const;

  /// Returns an adjusted number of \c FileIDs created within the specified \c

  /// FileID, accounting for any non-affecting input files.

  unsigned getAdjustedNumCreatedFIDs(FileID FID) const;

  /// Returns an adjusted \c SourceLocation, accounting for any non-affecting

  /// input files.

  SourceLocation getAdjustedLocation(SourceLocation Loc) const;

  /// Returns an adjusted \c SourceRange, accounting for any non-affecting input

  /// files.

  SourceRange getAdjustedRange(SourceRange Range) const;

  /// Returns an adjusted \c SourceLocation offset, accounting for any

  /// non-affecting input files.

  SourceLocation::UIntTy getAdjustedOffset(SourceLocation::UIntTy Offset) const;

  /// Returns an adjustment for offset into SourceManager, accounting for any

  /// non-affecting input files.

  SourceLocation::UIntTy getAdjustment(SourceLocation::UIntTy Offset) const;

  /// Retrieve or create a submodule ID for this module.

  unsigned getSubmoduleID(Module *Mod);

  /// Write the given subexpression to the bitstream.

  void WriteSubStmt(Stmt *S);

  void WriteBlockInfoBlock();

  void WriteControlBlock(Preprocessor &PP, ASTContext &Context,

                         StringRef isysroot);

  /// Write out the signature and diagnostic options, and return the signature.

  void writeUnhashedControlBlock(Preprocessor &PP, ASTContext &Context);

  ASTFileSignature backpatchSignature();

  /// Calculate hash of the pcm content.

  std::pair<ASTFileSignature, ASTFileSignature> createSignature() const;

  void WriteInputFiles(SourceManager &SourceMgr, HeaderSearchOptions &HSOpts);

  void WriteSourceManagerBlock(SourceManager &SourceMgr,

                               const Preprocessor &PP);

  void WritePreprocessor(const Preprocessor &PP, bool IsModule);

  void WriteHeaderSearch(const HeaderSearch &HS);

  void WritePreprocessorDetail(PreprocessingRecord &PPRec,

                               uint64_t MacroOffsetsBase);

  void WriteSubmodules(Module *WritingModule);

  void WritePragmaDiagnosticMappings(const DiagnosticsEngine &Diag,

                                     bool isModule);

  unsigned TypeExtQualAbbrev = 0;

  void WriteTypeAbbrevs();

  void WriteType(QualType T);

  bool isLookupResultExternal(StoredDeclsList &Result, DeclContext *DC);

  bool isLookupResultEntirelyExternal(StoredDeclsList &Result, DeclContext *DC);

  void GenerateNameLookupTable(const DeclContext *DC,

                               llvm::SmallVectorImpl<char> &LookupTable);

  uint64_t WriteDeclContextLexicalBlock(ASTContext &Context, DeclContext *DC);

  uint64_t WriteDeclContextVisibleBlock(ASTContext &Context, DeclContext *DC);

  void WriteTypeDeclOffsets();

  void WriteFileDeclIDsMap();

  void WriteComments();

  void WriteSelectors(Sema &SemaRef);

  void WriteReferencedSelectorsPool(Sema &SemaRef);

  void WriteIdentifierTable(Preprocessor &PP, IdentifierResolver &IdResolver,

                            bool IsModule);

  void WriteDeclUpdatesBlocks(RecordDataImpl &OffsetsRecord);

  void WriteDeclContextVisibleUpdate(const DeclContext *DC);

  void WriteFPPragmaOptions(const FPOptionsOverride &Opts);

  void WriteOpenCLExtensions(Sema &SemaRef);

  void WriteCUDAPragmas(Sema &SemaRef);

  void WriteObjCCategories();

  void WriteLateParsedTemplates(Sema &SemaRef);

  void WriteOptimizePragmaOptions(Sema &SemaRef);

  void WriteMSStructPragmaOptions(Sema &SemaRef);

  void WriteMSPointersToMembersPragmaOptions(Sema &SemaRef);

  void WritePackPragmaOptions(Sema &SemaRef);

  void WriteFloatControlPragmaOptions(Sema &SemaRef);

  void WriteModuleFileExtension(Sema &SemaRef,

                                ModuleFileExtensionWriter &Writer);

  unsigned DeclParmVarAbbrev = 0;

  unsigned DeclContextLexicalAbbrev = 0;

  unsigned DeclContextVisibleLookupAbbrev = 0;

  unsigned UpdateVisibleAbbrev = 0;

  unsigned DeclRecordAbbrev = 0;

  unsigned DeclTypedefAbbrev = 0;

  unsigned DeclVarAbbrev = 0;

  unsigned DeclFieldAbbrev = 0;

  unsigned DeclEnumAbbrev = 0;

  unsigned DeclObjCIvarAbbrev = 0;

  unsigned DeclCXXMethodAbbrev = 0;

  unsigned DeclDependentNonTemplateCXXMethodAbbrev = 0;

  unsigned DeclTemplateCXXMethodAbbrev = 0;

  unsigned DeclMemberSpecializedCXXMethodAbbrev = 0;

  unsigned DeclTemplateSpecializedCXXMethodAbbrev = 0;

  unsigned DeclDependentSpecializationCXXMethodAbbrev = 0;

  unsigned DeclTemplateTypeParmAbbrev = 0;

  unsigned DeclUsingShadowAbbrev = 0;

  unsigned DeclRefExprAbbrev = 0;

  unsigned CharacterLiteralAbbrev = 0;

  unsigned IntegerLiteralAbbrev = 0;

  unsigned ExprImplicitCastAbbrev = 0;

  unsigned BinaryOperatorAbbrev = 0;

  unsigned CompoundAssignOperatorAbbrev = 0;

  unsigned CallExprAbbrev = 0;

  unsigned CXXOperatorCallExprAbbrev = 0;

  unsigned CXXMemberCallExprAbbrev = 0;

  unsigned CompoundStmtAbbrev = 0;

  void WriteDeclAbbrevs();

  void WriteDecl(ASTContext &Context, Decl *D);

  ASTFileSignature WriteASTCore(Sema &SemaRef, StringRef isysroot,

                                Module *WritingModule);

public:

  /// Create a new precompiled header writer that outputs to

  /// the given bitstream.

  ASTWriter(llvm::BitstreamWriter &Stream, SmallVectorImpl<char> &Buffer,

            InMemoryModuleCache &ModuleCache,

            ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,

            bool IncludeTimestamps = true, bool BuildingImplicitModule = false);

  ~ASTWriter() override;

  ASTContext &getASTContext() const {

    assert(Context && "requested AST context when not writing AST");

    return *Context;

  }

  const LangOptions &getLangOpts() const;

  /// Get a timestamp for output into the AST file. The actual timestamp

  /// of the specified file may be ignored if we have been instructed to not

  /// include timestamps in the output file.

  time_t getTimestampForOutput(const FileEntry *E) const;

  /// Write a precompiled header for the given semantic analysis.

  ///

  /// \param SemaRef a reference to the semantic analysis object that processed

  /// the AST to be written into the precompiled header.

  ///

  /// \param WritingModule The module that we are writing. If null, we are

  /// writing a precompiled header.

  ///

  /// \param isysroot if non-empty, write a relocatable file whose headers

  /// are relative to the given system root. If we're writing a module, its

  /// build directory will be used in preference to this if both are available.

  ///

  /// \return the module signature, which eventually will be a hash of

  /// the module but currently is merely a random 32-bit number.

  ASTFileSignature WriteAST(Sema &SemaRef, StringRef OutputFile,

                            Module *WritingModule, StringRef isysroot,

                            bool ShouldCacheASTInMemory = false);

  /// Emit a token.

  void AddToken(const Token &Tok, RecordDataImpl &Record);

  /// Emit a AlignPackInfo.

  void AddAlignPackInfo(const Sema::AlignPackInfo &Info,

                        RecordDataImpl &Record);

  /// Emit a FileID.

  void AddFileID(FileID FID, RecordDataImpl &Record);

  /// Emit a source location.

  void AddSourceLocation(SourceLocation Loc, RecordDataImpl &Record,

                         LocSeq *Seq = nullptr);

  /// Emit a source range.

  void AddSourceRange(SourceRange Range, RecordDataImpl &Record,

                      LocSeq *Seq = nullptr);

  /// Emit a reference to an identifier.

  void AddIdentifierRef(const IdentifierInfo *II, RecordDataImpl &Record);

  /// Get the unique number used to refer to the given selector.

  serialization::SelectorID getSelectorRef(Selector Sel);

  /// Get the unique number used to refer to the given identifier.

  serialization::IdentID getIdentifierRef(const IdentifierInfo *II);

  /// Get the unique number used to refer to the given macro.

  serialization::MacroID getMacroRef(MacroInfo *MI, const IdentifierInfo *Name);

  /// Determine the ID of an already-emitted macro.

  serialization::MacroID getMacroID(MacroInfo *MI);

  uint32_t getMacroDirectivesOffset(const IdentifierInfo *Name);

  /// Emit a reference to a type.

  void AddTypeRef(QualType T, RecordDataImpl &Record);

  /// Force a type to be emitted and get its ID.

  serialization::TypeID GetOrCreateTypeID(QualType T);

  /// Determine the type ID of an already-emitted type.

  serialization::TypeID getTypeID(QualType T) const;

  /// Find the first local declaration of a given local redeclarable

  /// decl.

  const Decl *getFirstLocalDecl(const Decl *D);

  /// Is this a local declaration (that is, one that will be written to

  /// our AST file)? This is the case for declarations that are neither imported

  /// from another AST file nor predefined.

  bool IsLocalDecl(const Decl *D) {

    if (D->isFromASTFile())

      return false;

    auto I = DeclIDs.find(D);

    return (I == DeclIDs.end() ||

            I->second >= serialization::NUM_PREDEF_DECL_IDS);

  };

  /// Emit a reference to a declaration.

  void AddDeclRef(const Decl *D, RecordDataImpl &Record);

  /// Force a declaration to be emitted and get its ID.

  serialization::DeclID GetDeclRef(const Decl *D);

  /// Determine the declaration ID of an already-emitted

  /// declaration.

  serialization::DeclID getDeclID(const Decl *D);

  unsigned getAnonymousDeclarationNumber(const NamedDecl *D);

  /// Add a string to the given record.

  void AddString(StringRef Str, RecordDataImpl &Record);

  /// Convert a path from this build process into one that is appropriate

  /// for emission in the module file.

  bool PreparePathForOutput(SmallVectorImpl<char> &Path);

  /// Add a path to the given record.

  void AddPath(StringRef Path, RecordDataImpl &Record);

  /// Emit the current record with the given path as a blob.

  void EmitRecordWithPath(unsigned Abbrev, RecordDataRef Record,

                          StringRef Path);

  /// Add a version tuple to the given record

  void AddVersionTuple(const VersionTuple &Version, RecordDataImpl &Record);

  /// Retrieve or create a submodule ID for this module, or return 0 if

  /// the submodule is neither local (a submodle of the currently-written module)

  /// nor from an imported module.

  unsigned getLocalOrImportedSubmoduleID(const Module *Mod);

  /// Note that the identifier II occurs at the given offset

  /// within the identifier table.

  void SetIdentifierOffset(const IdentifierInfo *II, uint32_t Offset);

  /// Note that the selector Sel occurs at the given offset

  /// within the method pool/selector table.

  void SetSelectorOffset(Selector Sel, uint32_t Offset);

  /// Record an ID for the given switch-case statement.

  unsigned RecordSwitchCaseID(SwitchCase *S);

  /// Retrieve the ID for the given switch-case statement.

  unsigned getSwitchCaseID(SwitchCase *S);

  void ClearSwitchCaseIDs();

  unsigned getTypeExtQualAbbrev() const {

    return TypeExtQualAbbrev;

  }

  unsigned getDeclParmVarAbbrev() const { return DeclParmVarAbbrev; }

  unsigned getDeclRecordAbbrev() const { return DeclRecordAbbrev; }

  unsigned getDeclTypedefAbbrev() const { return DeclTypedefAbbrev; }

  unsigned getDeclVarAbbrev() const { return DeclVarAbbrev; }

  unsigned getDeclFieldAbbrev() const { return DeclFieldAbbrev; }

  unsigned getDeclEnumAbbrev() const { return DeclEnumAbbrev; }

  unsigned getDeclObjCIvarAbbrev() const { return DeclObjCIvarAbbrev; }

  unsigned getDeclCXXMethodAbbrev(FunctionDecl::TemplatedKind Kind) const {

    switch (Kind) {

    case FunctionDecl::TK_NonTemplate:

      return DeclCXXMethodAbbrev;

    case FunctionDecl::TK_FunctionTemplate:

      return DeclTemplateCXXMethodAbbrev;

    case FunctionDecl::TK_MemberSpecialization:

      return DeclMemberSpecializedCXXMethodAbbrev;

    case FunctionDecl::TK_FunctionTemplateSpecialization:

      return DeclTemplateSpecializedCXXMethodAbbrev;

    case FunctionDecl::TK_DependentNonTemplate:

      return DeclDependentNonTemplateCXXMethodAbbrev;

    case FunctionDecl::TK_DependentFunctionTemplateSpecialization:

      return DeclDependentSpecializationCXXMethodAbbrev;

    }

    llvm_unreachable("Unknwon Template Kind!");

  }

  unsigned getDeclTemplateTypeParmAbbrev() const {

    return DeclTemplateTypeParmAbbrev;

  }

  unsigned getDeclUsingShadowAbbrev() const { return DeclUsingShadowAbbrev; }

  unsigned getDeclRefExprAbbrev() const { return DeclRefExprAbbrev; }

  unsigned getCharacterLiteralAbbrev() const { return CharacterLiteralAbbrev; }

  unsigned getIntegerLiteralAbbrev() const { return IntegerLiteralAbbrev; }

  unsigned getExprImplicitCastAbbrev() const { return ExprImplicitCastAbbrev; }

  unsigned getBinaryOperatorAbbrev() const { return BinaryOperatorAbbrev; }

  unsigned getCompoundAssignOperatorAbbrev() const {

    return CompoundAssignOperatorAbbrev;

  }

  unsigned getCallExprAbbrev() const { return CallExprAbbrev; }

  unsigned getCXXOperatorCallExprAbbrev() { return CXXOperatorCallExprAbbrev; }

  unsigned getCXXMemberCallExprAbbrev() { return CXXMemberCallExprAbbrev; }

  unsigned getCompoundStmtAbbrev() const { return CompoundStmtAbbrev; }

  bool hasChain() const { return Chain; }

  ASTReader *getChain() const { return Chain; }

  bool isWritingStdCXXNamedModules() const {

    return WritingModule && WritingModule->isNamedModule();

  }

private:

  // ASTDeserializationListener implementation

  void ReaderInitialized(ASTReader *Reader) override;

  void IdentifierRead(serialization::IdentID ID, IdentifierInfo *II) override;

  void MacroRead(serialization::MacroID ID, MacroInfo *MI) override;

  void TypeRead(serialization::TypeIdx Idx, QualType T) override;

  void SelectorRead(serialization::SelectorID ID, Selector Sel) override;

  void MacroDefinitionRead(serialization::PreprocessedEntityID ID,

                           MacroDefinitionRecord *MD) override;

  void ModuleRead(serialization::SubmoduleID ID, Module *Mod) override;

  // ASTMutationListener implementation.

  void CompletedTagDefinition(const TagDecl *D) override;

  void AddedVisibleDecl(const DeclContext *DC, const Decl *D) override;

  void AddedCXXImplicitMember(const CXXRecordDecl *RD, const Decl *D) override;

  void AddedCXXTemplateSpecialization(

      const ClassTemplateDecl *TD,

      const ClassTemplateSpecializationDecl *D) override;

  void AddedCXXTemplateSpecialization(

      const VarTemplateDecl *TD,

      const VarTemplateSpecializationDecl *D) override;

  void AddedCXXTemplateSpecialization(const FunctionTemplateDecl *TD,

                                      const FunctionDecl *D) override;

  void ResolvedExceptionSpec(const FunctionDecl *FD) override;

  void DeducedReturnType(const FunctionDecl *FD, QualType ReturnType) override;

  void ResolvedOperatorDelete(const CXXDestructorDecl *DD,

                              const FunctionDecl *Delete,

                              Expr *ThisArg) override;

  void CompletedImplicitDefinition(const FunctionDecl *D) override;

  void InstantiationRequested(const ValueDecl *D) override;

  void VariableDefinitionInstantiated(const VarDecl *D) override;

  void FunctionDefinitionInstantiated(const FunctionDecl *D) override;

  void DefaultArgumentInstantiated(const ParmVarDecl *D) override;

  void DefaultMemberInitializerInstantiated(const FieldDecl *D) override;

  void AddedObjCCategoryToInterface(const ObjCCategoryDecl *CatD,

                                    const ObjCInterfaceDecl *IFD) override;

  void DeclarationMarkedUsed(const Decl *D) override;

  void DeclarationMarkedOpenMPThreadPrivate(const Decl *D) override;

  void DeclarationMarkedOpenMPDeclareTarget(const Decl *D,

                                            const Attr *Attr) override;

  void DeclarationMarkedOpenMPAllocate(const Decl *D, const Attr *A) override;

  void RedefinedHiddenDefinition(const NamedDecl *D, Module *M) override;

  void AddedAttributeToRecord(const Attr *Attr,

                              const RecordDecl *Record) override;

};

/// AST and semantic-analysis consumer that generates a

/// precompiled header from the parsed source code.

class PCHGenerator : public SemaConsumer {

  const Preprocessor &PP;

  std::string OutputFile;

  std::string isysroot;

  Sema *SemaPtr;

  std::shared_ptr<PCHBuffer> Buffer;

  llvm::BitstreamWriter Stream;

  ASTWriter Writer;

  bool AllowASTWithErrors;

  bool ShouldCacheASTInMemory;

protected:

  ASTWriter &getWriter() { return Writer; }

  const ASTWriter &getWriter() const { return Writer; }

  SmallVectorImpl<char> &getPCH() const { return Buffer->Data; }

public:

  PCHGenerator(const Preprocessor &PP, InMemoryModuleCache &ModuleCache,

               StringRef OutputFile, StringRef isysroot,

               std::shared_ptr<PCHBuffer> Buffer,

               ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,

               bool AllowASTWithErrors = false, bool IncludeTimestamps = true,

               bool BuildingImplicitModule = false,

               bool ShouldCacheASTInMemory = false);

  ~PCHGenerator() override;

  void InitializeSema(Sema &S) override { SemaPtr = &S; }

  void HandleTranslationUnit(ASTContext &Ctx) override;

  ASTMutationListener *GetASTMutationListener() override;

  ASTDeserializationListener *GetASTDeserializationListener() override;

  bool hasEmittedPCH() const { return Buffer->IsComplete; }

};

/// A simple helper class to pack several bits in order into (a) 32 bit

/// integer(s).

class BitsPacker {

  constexpr static uint32_t BitIndexUpbound = 32u;

public:

  BitsPacker() = default;

  BitsPacker(const BitsPacker &) = delete;

  BitsPacker(BitsPacker &&) = delete;

  BitsPacker operator=(const BitsPacker &) = delete;

  BitsPacker operator=(BitsPacker &&) = delete;

  ~BitsPacker() = default;

  bool canWriteNextNBits(uint32_t BitsWidth) const {

    return CurrentBitIndex + BitsWidth < BitIndexUpbound;

  }

  void reset(uint32_t Value) {

    UnderlyingValue = Value;

    CurrentBitIndex = 0;

  }

  void addBit(bool Value) { addBits(Value, 1); }

  void addBits(uint32_t Value, uint32_t BitsWidth) {

    assert(BitsWidth < BitIndexUpbound);

    assert((Value < (1u << BitsWidth)) && "Passing narrower bit width!");

    assert(canWriteNextNBits(BitsWidth) &&

           "Inserting too much bits into a value!");

    UnderlyingValue |= Value << CurrentBitIndex;

    CurrentBitIndex += BitsWidth;

  }

  operator uint32_t() { return UnderlyingValue; }

private:

  uint32_t UnderlyingValue = 0;

  uint32_t CurrentBitIndex = 0;

};

} // namespace clang

#endif // LLVM_CLANG_SERIALIZATION_ASTWRITER_H